The present invention relates to a graphic fluorescent display device; and, more particularly, to a graphic fluorescent display device incorporating therein a planar grid.
FIGS. 1A to 2B provide schematic views for illustrating the arrangements and operation methods of anodes and grids of conventional graphic fluorescent display devices.
FIG. 1A is a top view for showing the arrangement of the anodes and the grids, in which reference notations A11 to A52 represent anodes; G1 to G5, the grids; A1 and A2, two anode lead wires. And in FIG. 1A, only three rows of the anodes and five grids are described. Every second anodes in a same row are connected to a same anode lead wire. When viewed from top of the fluorescent display device, the anodes, grids and filaments (not shown) are vertically disposed in that order while maintaining certain distances therebetween. Electrons emitted from the filaments pass through the grids G1 to G5 and reach the anode A11 to A52.
In FIG. 1A, the grid G1 controls the anodes A11 and A12 and the gird G2 does the anodes A21 and A22. The grids G3 to G5 also function similarly.
FIG. 1B is a schematic view for explaining operation scheme of the graphic fluorescent display device shown in FIG. 1A.
For instance, in order to turn on the anode A22 to emit light, negative voltages are respectively applied to the grids G1, G3, G4 and G5 and the anode lead wire A1, while a positive voltage is respectively applied to the grid G2 and the anode lead wire A2. The electrons emitted from the filament can pass through the grid G2 but cannot pass through the remaining grids G1, G3, G4 and G5 since the electrons moving toward the grid G1, G3, G4 and G5 are repulsed by the negative electric fields created by negative voltages applied thereto. The electrons passing through the grid G2 can reach the anode A22 to which positive voltage is applied but cannot reach the anode A21 to which negative voltage is applied.
Since, however, the electrons moving toward the anode A22 are affected by the negative electric field generated by the grid G3 of negative potential, the electrons may not reach an edge part of the anode A22 adjacent to the grid G3. As a result, there occurs the so-called eclipse phenomenon where an anode has a dark spot at the edge adjacent to a neighboring grid.
Referring to FIG. 1C, there is illustrated another conventional graphic fluorescent display device having anodes controlled by three anode lead wires A1 to A3 wherein every third anodes are connected to a same anode lead wire.
For instance, if negative voltages are applied to grids G1, G3 and G4, while a positive voltage is applied to the grid G2, electrons emitted from filaments can pass through only the grid G2 as shown in FIG. 1C. Further, if the anode lead wires A1 and A3 are of positive potentials, the electrons can reach the anodes A22 and A32. In this case, since the electrons moving toward the anodes A22 and A32 are affected by negative electric fields generated by the grids G1 and G3 of negative potentials, the electrons may not reach an edge part of the anode A22 adjacent to the anode G1 and an edge part of the anode A32 adjacent to the anode G3. Therefore, such edge parts do not emit sufficient light, which results in dark streaks thereat (See, e.g., Japanese Laid-Open Publication Number JP63-35037).
Referring to FIGS. 2A and 2B, there are illustrated conventional operation methods employed in order to prevent the non-uniformity in the brightness of the fluorescent display device described above with reference to FIGS. 1A to 1C.
In FIGS. 2A and 2B, there are four anode lead wires A1 to A4 and every fourth anodes are connected to a same anode lead wire. Each of the grids G1 to G5 controls two anodes.
In FIG. 2A, the grids G2 and G3 are of positive potentials and the grids G1, G4 and G5 are of negative potentials. Since the anodes A22 and A31 are selected to emit light, the anode lead wires A1 and A4 are of positive potential. In this case, since the anodes A22 and A31 are away from the grids G1 and G4, the negative electric fields created by the grids G1 and G4 scarcely influence the passages of the electrons emitted from filaments to the anodes A22 and A31.
The arrangement of the anodes, the grids and the anode lead wires shown in FIG. 2B is identical to the one shown in FIG. 2A, but grid selection scheme is different from that of FIG. 2A.
In FIG. 2B, positive potentials are applied to the grids G2, G3 and G4 and negative potentials are applied to the grids G1 and G5. Since the anodes A31, A32 controlled by the grid G3 are selected to be turned on, positive potentials are applied to the anode lead wires A1 and A2. In this case, since the anodes A31 and A32 are away from the grids G1 and G5 of negative potential, the negative electric fields created by the grids G1 and G5 hardly influence the passages of the electrons emitted from the filaments to the anodes A31 and A32. Further, the effect of the negative electric fields created by the grids G1 and G5 is less than that described in FIG. 2A (See, e.g., Japanese Laid-open Publication supra).
In FIGS. 1A to 1C, the non-uniformity in the brightness due to electronic fields of neighboring grids may not be avoided. Such a non-uniformity problem can be avoided by the control schemes as shown in FIGS. 2A and 2B. However, the configurations of FIGS. 2A and 2B require one grid for every two anodes, even though the anodes are controlled by four anode lead wires. Resultantly, still a large number of grids are required, complicating the structure of a fluorescent display device with a large number of drivers of the grids. Further, a duty factor becomes lower to thereby decrease the luminance level of the device.
It is, therefore, an object of the present invention to eliminate the above-mentioned disadvantages of the prior art.
In accordance with the present invention, there is provided a fluorescent display device including:
a first substrate;
an insulating layer formed on the first substrate;
n columns or rows of m anodes, each anode having a fluorescent layer thereon;
Q anode lead wires provided for each column or row of the m anodes, every Qth anodes being connected to a same anode lead wire; and
z grids, z being a positive integer equal to or greater than m/Q but smaller than (m/Q)+1, formed on the insulating layer, each grid being arranged across the n columns of m anodes, each grid being provided with openings for each column or row of m anodes, each opening exposing a portion of the insulating layer and one anode being formed on the exposed portion of the insulating layer,
wherein the insulating layer, the anodes, the anode lead wires and grids are thin films.